1. Field of the Invention
The present invention relates to an aqueous ink for inkjet recording which is improved in bleeding on recording medium, provides an excellent image quality and exhibits an excellent handleability and safety.
2. Background Art
In recent years, following the spread of computers, inkjet printers are widely utilized for printing on paper, films, cloths, etc. in not only offices but also households.
The inkjet recording method includes a mode of applying a pressure by a piezoelectric element to discharge droplets; a mode of generating bubbles in an ink by heat to discharge droplets; a mode of using ultrasonic wave; and a mode of sucking and discharging droplets by electrostatic force. As ink compositions for such inkjet recording, aqueous inks, oil based inks, or solid (melt type) inks are used. Of these inks, aqueous inks are the main current from the standpoints of manufacture, handling, smell, safety, etc.
With respect to coloring agents that are used in these inkjet recording inks, there are requirements that they have high solubility in solvent; that they can undergo high-density recording; that they have good hue; that they have excellent fastness to light, heat, air, water, and chemicals; that they have good fixation to an image receiving material and hardly cause bleeding; that they have excellent preservability as an ink; that they have no toxicity; that they have high purity; and that they can be cheaply obtained. However, it is extremely difficult to seek coloring agents that can meet these requirements at high levels.
Though various inkjet dyes and pigments have already been proposed and actually used, it is the present state that coloring agents that can meet all of the requirements have not yet been discovered. According to the conventionally well known dyes and pigments to which color index (C.I.) numbers are assigned, it is difficult to reconcile hue and fastness required for inkjet recording inks.
With the trend toward the rise of capacity for electrostatic digital image data, there is a growing demand for recording of images having a higher precision and quality. In order to meet this demand, it is necessary to use smaller ink droplets and prevent the ink droplets attached to the recording layer from expanding. In particular, the prevention of bleeding of dye due to the expansion of ink droplets is limited so far as it relies mainly on the improvement of the recording layer. It has thus been desired to provide a means of inhibiting the bleeding of dye contained in the ink solution by using improvements in the ink composition and the drawing method.
As yellow dyes for inkjet recording there have heretofore been widely known direct azo dyes, acidic azo dyes, etc.
Techniques involving the use of C. I. Acid Yellow 17, C. I. Acid Yellow 23 and C. I. Acid Yellow 26 as acidic azo dye and C. I. Direct Yellow 86, C. I. Direct Yellow 120, C. I. Direct Yellow 132, etc. as direct azo dye in yellow inks for inkjet recording are disclosed in Patent References 1 and 2.
The dye of the invention is superior to these dyes with respect to fastness. Techniques involving the use of the dye of the invention as a yellow ink for inkjet recording are disclosed in Patent Reference 3, Japanese Patent Application Nos. 2002-131536, 2002-124832 and 2002-211683.
As a means of inhibiting the bleeding of dye by improving the ink solution, a method involving the rise of the viscosity of the ink solution, a method involving the use of a low dispersibility particulate coloring material, a method involving the incorporation of a mordant, etc. have been attempted. However, these methods cannot inhibit image bleeding, se-cure the age stability of the ink solution and prevent the clogging of the drawing nozzle at the same time.
[Patent Reference 1]
JP-A-55-150396
[Patent Reference 2]
JP-A-2001-240781
[Patent Reference 3]
JP-A-2001-279145